Lime hydrate with improved reactivity via additives

ABSTRACT

Systems and Methods to produce a lime hydrate sorbent composition formed of highly reactive lime hydrate (HRH) by adding compounds to the slaking water in a method that would produce a non-HRH, which will typically be a lime hydrate having citric acid reactivity as discussed above of more than ten seconds, to make the non-HRH an HRH, which is having a citric acid reactivity of less than or equal to ten seconds.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. patent application Ser. No.16/511,168 filed Jul. 15, 2019 which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/700,143 filed Jul. 18, 2018.The entire disclosure of all the above documents is herein incorporatedby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This disclosure relates generally to air pollution control processesaimed at controlling acid gases that are emitted from industrial,utility, incineration, or metallurgical process. Specifically, theformation of high reactivity calcium hydroxide (HRH) through theaddition of various materials to a traditionally manufactured calciumhydroxide (lime hydrate).

2. Description of the Related Art

Many efforts have been made to develop materials for improved capabilityfor cleaning or “scrubbing” flue gas or combustion exhaust. Most of theinterest in such scrubbing of flue gas is to eliminate particularcompositions, specifically acid gases, that contribute to particularlydetrimental known environmental effects, such as acid rain.

Flue gases are generally very complex chemical mixtures which comprise anumber of different compositions in different percentages depending onthe material being combusted, the type of combustion being performed,impurities present in the combustion process, and specifics of the fluedesign. However, the release of certain chemicals into the atmospherewhich commonly appear in flue gases is undesirable, and therefore therelease of those specific components is generally regulated bygovernments and controlled by those who perform the combustion.

Some of the chemicals that are subject to regulation are certain acidgases. A large number of acid gases are desired to be, and are, undercontrolled emission standards in the United States and other countries.This includes compounds such as, but not limited to, hydrogen chloride(HCl), sulfur dioxide (SO₂) and sulfur trioxide (SO₃). Sulfur trioxidecan evidence itself as condensable particulate in the form of sulfuricacid (H₂SO₄). Condensable particulate can also be a regulated emission.

Flue gas exhaust mitigation is generally performed by devices called“scrubbers”. Scrubbers introduce chemical compounds into the flue gas.The compounds then react with the undesirable compounds which areintended to be removed by the reaction. Through these reactions, theundesirable compounds are either captured and disposed of, or turnedinto a less harmful compound prior to their exhaust, or both. Inaddition to controlling the emissions for environmental reasons, it isdesirable for many combustion plant operators to remove acid gases fromthe plant's flue gas to prevent the acid gases from forming powerfulcorroding compounds which can damage flues and other equipment.

These acid gases can arise from a number of different combustionmaterials, but are fairly common in fossil fuel combustion (such as oilor coal) due to sulfur being present as a common contaminant in the rawfuel. Most fossil fuels contain some quantity of sulfur. Duringcombustion, sulfur in the fossil fuel can oxidize to form sulfur oxides.A majority of these oxides forms sulfur dioxide (SO₂), but a smallamount of sulfur trioxide (SO₃) can also be formed. Particularly in coalcombustion, where the chemical properties of the coal are often highlydependent on where it is mined, the ability to mitigate the amount ofsulfur oxides in flue gas is highly desirable as it allows for lowerquality raw coal (which may be less expensive to produce and moreabundant) to be burned sufficiently cleanly to lessen environmentalimpact and impact on machinery.

FIG. 1 shows a loose block diagram of an arrangement of a flue gas ductsystem such as can be used in a coal fired power plant. Generally, majorcomponents include the boiler (101), a Selected Catalytic Reduction(SCR) system for reducing NO_(x) emissions (103), an Air Preheater (APH)(105), a particulate removal system (107) such as an electrostaticprecipitator (ESP) or baghouse, a Flue Gas Desulfurization (FGD) unit(109), and then the exhaust stack (111).

While the process for controlling acid gases is relatively simple,mitigation of undesirable compounds can be very difficult. Because ofthe required throughput of a power generation facility, flue gases oftenmove through the flue very fast and, thus, are present in the area ofscrubbers for only a short period of time. Further, many scrubbingmaterials (sorbents) often present their own problems. Specifically,having too much of the sorbent can cause problems with the plant'soperation from the sorbent clogging other components, building up onmoving parts, or from undesired later reactions with other sorbentsintroduced later into the flue gas. The problems of accurate scrubbingare particularly acute where the amount of acid gases produced may vary,where the time for reaction is very short, where the reaction needs tooccur “in-flight” within the flue gas, and where non-reacted sorbent cancause problems downstream. Many, if not all, of these concerns can occurin smaller facilities that may lack the scale to avoid them.

The presence of acid gases in flue gas also dictates operationaldecisions and increases operating costs with many tradeoffs.Minimization of SO₂ conversion to SO₃ may warrant the extra expense oflow conversion catalyst in Selective Catalyst Reduction (SCR) equipment.Fear of forming sticky ammonium bisulfate (ABS) particles on AirPreheater (APH) internals will affect operation of the SCR in order tocontain ammonia slip. The need to operate safely above dew point in theAPH also increases heat rate and resulting energy costs. Greater airflow due to a high heat rate translates to additional power required torun the fans. Further, ash release from baghouse bags can be lessefficient if the acid gases are untreated. Finally, units equipped withwet Flue Gas Desulfurization (FGD) will remove HCl, but the chlorides inthe wet system can lead to corrosion issues or additional processing inwater treatment.

Flue gas treatment has become a focus of electric utilities andindustrial operations due to increasingly tighter air quality standards.As companies seek to comply with air quality regulations usingcost-effective fuels, the need arises for effective flue gas treatmentoptions. Alkali species based on alkali or alkaline earth metals arecommon sorbents used to neutralize the acid components of the flue gas.The most common of these alkalis are sodium, calcium, ormagnesium-based. A common method of introduction of the sorbents intothe gas stream is to use Dry Sorbent Injections (DSI). The sorbents areprepared as a fine or coarse powder and transported and stored at theuse site. DSI systems pneumatically convey powdered sorbents to form afine powder dispersion in the duct.

Much of the efficiency of DSI equipment is dictated by the ability ofthe injection system to have the sorbent contact the acidic componentsof the flue gas in-flight or while the flue gas is moving through theduct. Flue gas pathways are not homogeneous in nature, as structuralcomponents of the flue, wall effects, and combustion processes provide aflue gas stream that can be stratified horizontally or vertically. It isthe job of the DSI system to put the sorbent where the acid gas travelsand the sorbent needs to react sufficiently quickly with the target acidgases so as to have the reaction completed before the gas moves into asection of the duct where the spent sorbent is removed (if necessary).Sorbent which does not enter the zones where acid is concentrated isfree to react with other components of the flue gas or remain unreacteduntil removed in particulate collection.

One proposed material for use in scrubbing of acid gases is increaseduse of calcium hydroxide (lime hydrate). It has been established thatlime hydrate can provide a desirable reaction to act as a mitigationagent for a number of acid gases and lime hydrate systems have provensuccessful in many full-scale operations. Typically, lime hydrate hasbeen used in sorbent beds, where the flue gas passes through or over thebed to react out the acid gases present therein. The problem with thistype of use, however, is two-fold. Firstly, beds are limited topositions in which they can be used and secondly, it has inhibited limehydrate from being used in in-flight injections systems, such as a DSI.

The problem with in-flight use of lime hydrate has been that traditionallime hydrate is often not reactive enough (that is, it does not reactquick enough) to neutralize sufficient acid gas in-flight without theneed to provide excess material the presence of which can causedownstream problems. This is not because the lime hydrate as a chemicaldoes not react fast enough, but because in-flight reactivity appears tobe very dependent on properties of the particulate compound which thelime hydrate is formed into.

SUMMARY OF THE INVENTION

The following is a summary of the invention, which should provide to thereader a basic understanding of some aspects of the invention. Thissummary is not intended to identify critical elements of the inventionor in any way to delineate the scope of the invention. The sole purposeof this summary is to present in simplified text some aspects of theinvention as a prelude to the more detailed description presented below.

Because of these and other problems in the art, there is describedherein, among other things, air pollution control processes aimed atcontrolling acid gases that are emitted from industrial, utility,incineration, or metallurgical process. Specifically, the formation ofhigh reactivity calcium hydroxide (HRH) through the addition of variousmaterials to a traditionally manufactured calcium hydroxide (limehydrate) that lacks the reactivity of HRH to improve the reactivity oftraditionally manufactured lime hydrate allowing for it to be used insituations best suited for an HRH. It also discusses utilizing the sameadditives in the production of prior HRHs to produce even higherreactivity lime hydrates referred to as Super Reactive Hydrates (SRH).

There is described herein, in an embodiment, a method for forming asorbent composition with improved acid gas reactivity comprising:forming a calcium oxide particulate; slaking the calcium oxideparticulate with water and an additive to form calcium hydroxideparticles; and forming a sorbent composition from the calcium hydroxideparticles; wherein the additive is selected from the group consistingof: an additive to increase BET surface area; an additive to increasereactivity, or both additives; wherein the calcium hydroxide particleshave a reactivity of less than 10 seconds and a BET surface area of 20m²/g or greater; and wherein the reactivity is an amount of time ittakes the calcium hydroxide particles to neutralize in citric acid, thecitric acid having a mass greater than 10 times a mass of the calciumhydroxide particles.

In various embodiments of the method, the reactivity is less than 8seconds, less than 4 seconds, less than 3 seconds, or between about 2seconds and about 5 seconds.

In an embodiment of the method, the mass of the calcium hydroxideparticles is about 1.7 grams and mass of citric acid is about 26 grams.In various embodiments of this method, the reactivity is less than 8seconds, less than 4 seconds, less than 3 seconds, or between about 2seconds and about 5 seconds.

In an embodiment of the method, the sorbent composition comprises atleast 95% calcium hydroxide particles.

In an embodiment of the method, the additive to increase reactivity isselected from the group consisting of: sugars and lignosulfonate salts.

In an embodiment of the method, the additive to increase reactivity isbetween 0.75% to 1.25% of the calcium oxide feed by weight.

In an embodiment of the method, the additive to increase BET surfacearea is selected from the group consisting of: glycols derived fromethylene oxide and amines produced from reacting ethylene oxide withammonia.

In an embodiment of the method, the additive to increase BET surfacearea is between 0.5% to 3% of the calcium oxide feed by weight.

There is also described herein, in an embodiment, a method for forming asorbent composition with improved acid gas reactivity comprising:forming a calcium oxide particulate; selecting a slaking and millingprocess to form calcium hydroxide particles, the calcium hydroxideparticles formed from the selected slaking and milling process having atleast one of: a reactivity of more than 10 seconds or a BET surface areaof 20 m²/g or less; altering the slaking process to include an additive,the calcium hydroxide particles formed from the altered slaking andmilling process having both a reactivity of less than 10 seconds and aBET surface area of 20 m²/g or more; and forming a sorbent compositionfrom the calcium hydroxide particles produced from the altered slakingand milling process; wherein the additive is selected from the groupconsisting of: an additive to increase BET surface area; an additive toincrease reactivity, or both additives; and wherein the reactivity is anamount of time it takes the calcium hydroxide particles to neutralize incitric acid, the citric acid having a mass greater than 10 times a massof the calcium hydroxide particles.

In an embodiment of the method, the additive to increase reactivity isselected from the group consisting of: sugars and lignosulfonate salts.

In an embodiment of the method, the additive to increase reactivity isbetween 0.75% to 1.25% of the calcium oxide feed by weight.

In an embodiment of the method, the additive to increase BET surfacearea is selected from the group consisting of: glycols derived fromethylene oxide and amines produced from reacting ethylene oxide withammonia.

In an embodiment of the method, the additive to increase BET surfacearea is between 0.5% to 3% of the calcium oxide feed by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a conceptual block diagram of an embodiment of a fluegas duct system as may be used in, for example, a coal fired powerplant.

FIG. 2 depicts a block diagram of an embodiment of a method ofmanufacturing lime hydrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Lime hydrate particulate compounds have traditionally been manufacturedaccording to a commonly known and utilized process. First, a lime feed(limestone) is heated in a lime kiln to a temperature above 825° C.where calcium oxide (commonly known as quicklime) is formed inaccordance with the following formula:

CaCO₃(s)→CaO(s)+CO₂(g)

The quicklime is then continuously grinded using a pulverizing milluntil a certain percentage of all the ground particles meet a desiredsize (e.g., 95% or smaller than 100 mesh). Second, the quicklime meetingthe desired size requirements is then fed into a hydrator, where thecalcium oxide reacts with water (also known as slaking), and thenquickly dried to form calcium hydroxide in accordance with the followingequation:

CaO+H₂O→Ca(OH)₂

Finally, the resultant calcium hydroxide (also known as lime hydrate) isthen milled and classified until it meets a desired level of fineness orsurface area for the target process.

As can be seen from the above, physical properties of the resultant limehydrate particulate compound such as, but not limited to, particle sizedistribution, mean particle size, amount of lime hydrate versus othercompounds, and other “structural” factors are often dictated by twoprimary elements of the process, the composition of the initial limefeed and the resultant milling and classifying processes.

The reaction of a particulate lime hydrate composition with an acid gas(such as SO₂) is generally assumed to follow the diffusion mechanism.The acid gas removal is the diffusion of acid gas from the bulk gas tothe sorbent particles. Thus, the total surface area of the composition(which is related to the mean particle size and particle sizedistribution within the composition) is believed to be very important.Specially, increased surface area implies faster reaction time and thus,compositions with particles which are smaller than compositions withparticles which are larger should be more reactive and better at acidgas mitigation. However, in practice, while high surface area (asrepresented by smaller particle size) is important, a small particlesize composition alone has proven to not warrant a prediction ofimproved removal of acid gases. Thus, the old wisdom on how to make limehydrate more reactive (which is simply to grind it into smaller andsmaller particles) does not really work.

Instead, surface area of a lime hydrate particulate composition has nowturned to a more sophisticated calculation which takes into account theshape of the particles within the composition to better determine thecomposition's reactivity to acid gases when injected as a dry sorbent.This calculation is referred to as the “BET surface area” of the limehydrate particulate composition. BET surface area is generally adetermination of surface area based on the theories of Stephen Brunauer,Paul Hugh Emmett, and Edward Teller (commonly called BET theory anddiscussed in S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc.,1938, 60, 309, the entire disclosure of which is herein incorporated byreference). This methodology particularly focuses on the availablesurface area of a solid for absorbing gases—recognizing that surfacearea, in such circumstances, can be increased by the presence of poresand related structures. BET, therefore, takes into account that thetotal surface area of a spray of particles is not only dependent on thesize of the particles, but is dependent on their “shape” in thatparticles with lots of holes (pores) can have a greater surface areathan their size would imply.

Because of the recognition that BET surface area is a better indicatorof available surface area for reaction, commercially available hydrateproducts have focused on obtaining lime hydrate with particularly highBET surface areas and this is believed to be necessary to provide foreffective absorption. It is generally believed that the BET surface areareally needs to be above 20 m²/g to be effective for acid gas removal,and in many recent lime hydrate compositions the BET surface area isabove 30 m²/g to attempt to continue to improve efficiency. Two examplesof lime hydrate compositions with increased BET surface areas aredescribed in U.S. Utility U.S. Pat. Nos. 5,492,685 and 7,744,678, theentire disclosures of which are herein incorporated by reference.

While the industry is focused on BET surface area as a proxy for limereactivity with acid gases, the BET surface area also does not seem totell the whole story. In particular, while a BET surface area above acertain threshold seems to be necessary for good reactivity, continuingto try and increase the BET surface area has led to diminishing returnsand in fact a reversal of reactivity in some cases. This has led to abelief that not only is the total BET surface area relevant, but theactual shape and style of the pores is also important. Specifically, thehigh pore volume of large pores (e.g. particles with large holes inthem) has generally been believed to be required to minimize the poreplugging effect during reaction and, therefore, while BET surface areahas been determined to be a reasonable proxy for effectiveness of limehydrates in removal of acid gases, it is not an ideal one.

When the reaction time is limited and the speed of reactivity of thelime hydrate particulate composition is important, as it often is forduct areas that require in-flight capture of acid gases, it appears thatthe external surface area of the particle may actually be more importantthan the internal surface area (as measured by the BET gas adsorptionprocess). The external surface area of the distribution of particles isan indication of the actual size of the hydrate particle as opposed toits available surface area. As the external or relative surface sizeincreases the particle size generally decreases. In contrast to largeparticles that may have a high total surface area, it is the outersurface of ultrafine particles that hold most of the free reactants thatare believed needed for the actual reaction. Thus, one is returned tothe presumption that the smaller the individual particles in thecomposition, the more effective the removal of acid gases.

As discussed previously, however, this does not appear to tell the wholestory. In many cases extremely small particles, while having highexternal surface area overall, are actually less reactive than particleswhich are larger and have less external surface area. Because it appearsto be the case that either traditional measure of surface area (smalleroverall particle size or BET surface area of the composition) cannotaccurately predict effective highly reactive compounds, it has becomenecessary to instead classify particulate compositions based on theiractual acid reactivity, instead of focusing on the surface area of thecomposition as a proxy.

Without being bound to any particular theory of operation, the problemwith utilizing surface area of particulates as a proxy for reactivityappears to be that lime particulate compounds are not uniform andchanges (particularly to distribution of particle size and BET surfaceareas) within the particulate distributions may be the best predictorsof actual reactivity speed during dry injection type processes. Nocommercially viable lime particulate compound for use in acid gasreactivity includes particles of uniform size or surface area as suchmaterials are commercially impractical (if not impossible) to produce.Instead, the compounds are made up of particles with a variety of sizesand surface areas. This phenomenon is well known and is part of analysisof particulate compounds. However, it has led to understanding that theproperties of the compound viewed as a whole, and not necessarily anyparticular particles within it, may decide the reactivity.

Because of this, it has been desirable to determine the actualreactivity of specific lime hydrate particulate compounds. As discussedin U.S. patent application Ser. No. 15/344,173, the entire disclosure ofwhich is herein incorporated by reference, in order to test reactivityof particular lime hydrate compounds, in an embodiment, the reactivityof the compound to a weak acid (such as, but not limited to, citricacid) provides for a reactivity time that is measurable with commercialinstruments. The problem with determining reaction time to strongeracids is that the reaction can often be too quick to effectively measureat laboratory scaling. Thus, it is difficult to predict compositionsthat will function well without performing large scale pilot testing. Inorder to determine the citric acid reactivity of a particular limehydrate composition, the amount of time it took 1.7 grams of limehydrate to neutralize 26 grams of citric acid is measured. As ameasurement of effectiveness, it is preferred that this value be lessthan or equal to 10 seconds in order to have a lime hydrate compositionwhich is classified as being “highly reactive”. However in analternative embodiment it can be less than 8 seconds. It is morepreferred that this value be 4 or less, 3 or less, 2 or less or 1 orless. Again, given the practical realities that production of improvedmaterial often results in a product having dramatically increased costsof products, utilizing current manufacturing techniques and for currentemissions standards, in an embodiment particularly effective limehydrates may be in the 2-5 second range, or, in another embodiment, inthe 3-4 second range.

Highly Reactive Hydrate (or HRH) is a classification of lime hydratecompounds where the classification may be obtained based, in part, oncitric acid reactivity. HRHs may be defined (in addition or inalternative to other methods) based on the citric acid reactivity of thecompound (as discussed above) being less than 10 seconds or any of thefaster time thresholds contemplated above. HRHs will also typically haveBET surface areas above 20 m²/g making them suitable for at least someuses based solely on their BET surface area. However, many HRHs willhave BET surface areas above 30 m²/g and such a particularly high BETsurface area can actually serve to define an HRH in some cases.

HRHs are generally capable of acid neutralization in ways thattraditional lime hydrates (being classified, for example, by beingmilled and classified solely to reach a target BET surface area of theresultant composition) are not. For example, HRH can typically be usedin applications which require in-flight neutralization of acid gas, andcan be used in applications where a lower quantity of hydrate needs tobe used to avoid clogging downstream elements of the flue duct withparticulates. Traditionally manufactured lime hydrates, even if milledand classified to segregate a portion which meets HRH level BET surfacearea criteria, cannot be used in these circumstances because they simplyare insufficiently reactive.

Because the traditional logic of “mill and classify” until a resultantcomposition with the desired BET surface area characteristic is obtaineddoes not consistently or predictably produce HRH compositions, theobtaining of HRH compositions has previously focused on modifications tothe process of producing lime hydrate which result in the production ofHRH compositions. Such processes for producing an HRH directly aredescribed in, for example, U.S. Pat. No. 9,517,471 and U.S. patentapplication Ser. Nos. 14/289,278; 14/541,850; 15/466,097; and Ser. No.15/596,911, the entire disclosure of all of which is herein incorporatedby reference. These processes produce lime hydrate particulatecompositions that can perform as necessary to be classified as HRH,generally by citric acid reactivity, BET surface area, or a combinationof both. However, these processes are often more manufacturing intensiveand require more stages of manufacturing than the manufacture oftraditional lime hydrates.

While all the above are perfectly acceptable ways to produce HRH, it isdesirable to be able to produce HRH without having to utilize anymodified manufacturing methodology, but to instead to utilize thetraditional mill, hydrate, mill and classify process as discussed above.

One way to utilize traditional milling and hydration techniques toproduce an HRH is to add compounds to a non-HRH lime hydrate, which willtypically be a lime hydrate having citric acid reactivity as discussedabove of more than ten seconds, to make the non-HRH an HRH, which ishaving a citric acid reactivity of less than or equal to ten seconds.Additionally, these types of additions can provide for adding compoundsto an already HRH lime hydrate, which is a lime hydrate having citricacid reactivity as discussed above of less than 10 seconds, to increasethe reactivity of the HRH to twice what it was and less than or equal to5 seconds.

The systems and methods discussed herein effectively allow one to“upconvert” traditional (or non-HRH) lime hydrate into HRH. This type ofsystem would allow for facilities that lack the specific machinery ortechniques for producing HRH according to any more specific methodologyto produce HRH by simply manufacturing a lime hydrate by traditionalprocesses, and then turning it into an HRH.

Further, some lime hydrates (whether HRH or not) may have additivesadded to them to provide particular beneficial secondary chemicalproperties to them having nothing to do with reactivity speed. Forexample, sodium compounds may be added to provide for a reducedresistivity of the HRH to allow the HRH to be used around an ESP ascontemplated in U.S. patent application Ser. No. 16/235,885 the entiredisclosure of which is herein incorporated by reference. While inclusionof these additives can allow for the lime hydrate composition to be usedin specific applications where it may not have been useable before,these additives can result in a prior HRH material no longer reactingfast enough to be considered an HRH, or can result in a non-HRH limehydrate compound reducing its reactivity even further. Regardless, whatcan happen is that the additive is necessary to provide onecharacteristic to the composition to make is suitable for a particularuse, while the same additive reduces a different characteristic of thecomposition to the point where the composition is no longer useful forthat same use. In these circumstances, the ability to both keep thecharacteristic added by the additive, and allow the material to maintainor improve its reactivity is desirable.

Finally, to the extent that a traditional lime hydrate can be“upconverted” to an HRH, those same processes can be used on productswhich are produced as HRH using the specific methods contemplated above(or other later developed methods) to further increase the reactivity ofproducts which are already defined as an HRH to increase the reactivityof the HRH to previously unavailable levels. This can produce what isreferred to herein as Super Reactive Hydrates (SRH), a subcategory ofHRH, where the citric acid reactivity can be reduced to below 5 seconds,4 seconds, 3 seconds, 2 seconds, 1 seconds, or lower and/or the BETsurface area can be increased to 40 m²/g, 50 m²/g, 60 m²/g, 70 m²/g, orhigher. SRH can be useable in reactions where traditional lime hydrateis simply unusable due to reaction speed making SRH effectively a wholenew option for lime hydrate use in a variety of industries andapplications.

Turning now to FIG. 2, a general block diagram of the method ofmanufacturing lime hydrate including an additive addition for improvingreactivity will be described in more detail in accordance with severalembodiments. After a lime feed (40) has been heated in a lime kiln (41)to a temperature above 825° C., quicklime (50) is formed. The quicklime(50) is subjected to fine grinding or milling (10) to produce a finelime (53). The fine lime (53) can be of varying sizes in differentembodiments. Any grinding or milling is suitable, including, forexample, fine grind cage mill, swing hammer mill, screen mill, etc.where the amount of milling produces the desired particle-sizedistribution. The fine lime (53) (and resultant steps) may also beproduced and performed using the methodology of U.S. Utility patentapplication Ser. No. 15/596,911, the entire disclosure of which isherein incorporated by reference.

In an embodiment, the fine lime (53) will have a particle-sizedistribution of greater than about 80% minus 200 mesh. In anotherembodiment, it will be greater than 93.5% minus 200 mesh. It should alsobe noted that, although the prior description refers to particlespassing through a mesh, this description and use of mesh merely refersto the common use of the term “mesh” as it relates to particle-sizedistribution. A mesh screen or sieve need not be used to measure orclassify the particle-size (although it is suitable in someembodiments). Instead, an air classification system is preferably used.

As quicklime is generally not stable and, when cooled, willspontaneously react with CO₂ from the air until, after enough time, itis completely converted back to calcium carbonate. All the milling andclassification of the quicklime (50) should preferably be producedentirely in a closed-circuit system to prevent air slaking andrecarbonation (i.e., CaO to CaCO₃) from occurring, although aclosed-circuit system is by no means required. In some embodiments,additional measures are employed to prevent recarbonation. For example,conditioned low CO₂ air (18) can be injected (66) into these systems toreplace any air being drawn in and around process equipment bearings andseals. This conditioned air (18) is also very useful if the quicklimeneeds to be pneumatically conveyed. The process for conditioning thisair is discussed more fully below and is also described in U.S. UtilityU.S. Pat. No. 6,200,543 (the entire disclosure of which is incorporatedherein by reference).

As noted above, the fine lime (53) then undergoes a hydration or slakingprocess. The hydration process generally utilizes a hydrator (12), andin a preferred embodiment, the fine lime (53) is combined with an excessof water (54), which may include any additives (55), and is rapidlymixed, which allows the fine lime (53) to react with the water (54) toform a wet or damp calcium hydroxide composition (56) which will nowalso include the additives (55). These additives (55) may be to providedifferent characteristics, as part of the “upconverting” process formaking HRH from non-HRH, for making SRH from HRH, or for countering adecreased reactivity effect of another additive so included.

The water (54) for hydration is generally fed at a reasonably hightemperature but low enough that the refined fine lime (53) is notoverheated (burned). In this regard, the water feed (54) and hydrator(12) temperature should be maintained below the boiling point of water,and more preferably, at a temperature equal to or below 180° F.Utilizing an excess of water (i.e., more than necessary to react withthe CaO but at a controlled percentage as known to those of ordinaryskill in the art) also helps prevent overheating and burning and helpsseparate the individual particles. In any event, in one embodiment, thedamp lime hydrate (56) that leaves the hydrator (12) has a residualmoisture greater than 5%. Generally, the water level will be about 5-35%or about 10-25%. Alternatively, the residual moisture may besubstantially lower and, in another embodiment, may be in the range ofabout 2% to about 4%. In this latter case, or even if residual water islower, the residual water may actually be pushed off as steam via theheat of the slaking reaction. Effectively, correctly choosing the rightamount of water can result in a “dry” hydrate being produced as theexcess water provided is essentially the amount needed to cool thereaction and the act of cooling the reaction causes all the water to bedriven off as steam.

As indicated above, traditional additives (55) may be included in thewater feed (54) that is utilized in the hydration process (53). Theseadditives are generally accelerators or retarders, which, as their namessuggest, accelerate or retard the reaction of calcium oxide to calciumhydroxide. Any known accelerators or retarders can be utilized,including, alkaline-earth chlorides (e.g., barium chloride, calciumchloride, sodium chloride, potassium chloride, aluminum chloride, etc.),other salts (e.g., aluminum nitrate, sodium carbonate, sodium borate,potassium permanganate, potassium chlorate, table salt, Rochelle salt,etc.), acids (e.g., hydrochloric acid, sulfuric acid, oxalic acid,nitric acid, acetic acid, lactic acid, etc.), alkanols (e.g., mono-,di-, and tri-ethanolamine, dimethylethanolamine, methyl diethanolamine,triisopropanolamine, etc.), and sugars. Further examples of suchaccelerators and retarders, and their use in lime hydrate production canbe found in U.S. Pat. Nos. 1,583,759; 1,649,602; 1,664,598; 2,193,391;2,423,335; 2,437,842; 3,120,440; 4,626,418; 4,786,485; 5,173,279;5,306,475; 5,308,534; 5,332,436; 5,502,021; 5,618,508; 5,705,141;6,322,769; and 7,744,678 (the entire disclosures of which areincorporated herein by reference).

Other additives can be added to the slaking water to give the limehydrate specific properties. For example, as contemplated in U.S. patentapplication Ser. No. 16/235,885 sodium metal and/or sodium compoundssuch as, but not limited to, sodium carbonate (Na₂CO₃), sodium hydroxide(NaOH), sodium bicarbonate (NaHCO₃), and/or Trona (Na₂CO₃—NaHCO₃—2H₂O),is added to a lime hydrate composition to lower the resistivity of theresultant hydrate compound.

After the lime has been slaked to form a damp lime hydrate (56), thedamp lime hydrate (56) is then dried in a heat dryer (14) if that isnecessary. In a preferred embodiment, the damp lime hydrate (56) isflash-dried using air (64) from an indirect heat source (17) with atemperature of about 550° F. to about 850° F. Using indirect heatprevents the hydrate composition from contacting the combustion gaswhich can occur if a direct heat source were to be used. This contactwould result in the loss of some of the available calcium hydroxide. Inany event, the dried lime hydrate (57) generally will have a residualmoisture content of about 1% or less.

As noted above, the presence of CO₂ in air which then comes in contactwith the lime hydrate can compromise the chemical integrity of the limehydrate. While lime hydrate has greater moisture stability than calciumoxide, lime hydrate is perishable unless adequately protected from CO₂absorption and the introduction of CO₂ into the lime hydrate can resultin recarbonation (i.e., Ca(OH)₂ to CaCO₃). Thus, in some embodiments,the chemical purity can be further improved if the indirect heater (17)is supplied with conditioned air (63) that has a reduced CO₂ content.Examples of apparatuses and methods for such air conditioning (i.e.,reduction of CO₂ content in the air stream) are disclosed, for example,in U.S. Pat. Nos. 5,678,959 and 6,200,543 (the entire disclosures ofwhich are incorporated herein by reference). In one preferredembodiment, ambient air (65) (e.g., about 300 ppm CO₂) is fed into anair conditioner (18), resulting in conditioned air (63) with a CO₂concentration of less than 100 ppm CO₂.

As noted above, conditioned air (66) with the same or different CO₂concentrations as the conditioned air (63) for drying can also be fedinto the mill (10) and/or hydrator (12) to help prevent recarbonation.Additionally, conditioned air (61) can be fed into any additionalclassifiers (15) and/or mills (16) as discussed more fully below.

After being dried (14) (as necessary), the dried lime hydrate (57) isthen preferably classified (15) and milled (16). The dried lime hydrate(57) is first fed into a classifier (15). If it meets the desiredproperties (e.g. BET surface area, and particle size), dried limehydrate (57) is utilized as the final lime hydrate product (60). Some ofthe dried lime hydrate (57), however, may not meet the desiredproperties. This non-final lime hydrate (58) is then fed into the mill(16) to be grinded, with the grinded lime hydrate (59) being fed backinto the classifier (15) to determine if the material can be utilized asthe final lime hydrate product (60). This process of milling (16) andclassifying (15) can generally continue for as long as is necessary.

Again, in a preferred embodiment, the milling (15) and classificationsystem (16) are conducted in a closed circuit system to prevent aircarbonation from occurring. Conditioned air (61) (i.e., low CO₂) canfurther be injected into the milling (15) and classification system (16)to replace any transient air being drawn into the process and preventrecarbonation.

The above process of manufacturing describes a process in which thedrying (14), classifying (15), and milling (16) of the damp lime hydrate(56) are conducted independently. As would be understood by one ofordinary skill in the art, milling and classification system can be, andcommonly are, integrated into one system wherein dried lime hydrate (57)is fed into the milling/classification system with injected conditionedair (61) and the resultant final lime hydrate product (60) has thedesired properties as discussed above. Similarly, an integrated millingand classification system can be further integrated into a dryer whereinthe damp lime hydrate (56) is fed into the milling/classification/dryersystem with an indirect heat source (17) and the resultant final limehydrate product (60) has the desired properties as discussed above.

In any event, embodiments of the manufacturing process described hereinresult in a final lime hydrate product (60) (sorbent compound) with ahigh purity and good reactivity. In particular embodiments, the finallime hydrate product (60) will generally have a purity of 96% calciumhydroxide or greater and a particle size of less than about 44 microns(325 mesh) for about 98% of the particles. However, these lime hydrateswill also have a citric acid reactivity of less than 10 seconds and/or aBET surface area of above 30 m²/g for an HRH classified result or acitric acid reactivity of less than 5 seconds and/or a BET surface areaof above 40 m²/g for an SRH product.

As contemplated above, the HRH products and SRH products produced bythese systems and methods will typically be produced through theaddition of the specific additives as part of the slaking water and thetype of additional additives provided often depends on thecharacteristic the resultant lime hydrate would have that would inhibitit from being considered an HRH or SRH. As discussed above, HRH isgenerally defined as having citric acid reactivity of less than 10seconds and/or a BET surface area of above 30 m²/g and an SRH isgenerally defined as having a citric acid reactivity of less than 5seconds and/or a BET surface area of above 40 m²/g. As it is preferredthat both an HRH and SRH have both characteristics (citric acidreactivity and BET surface area) of their respective classification,additives will be discussed which can be used to increase BET surfacearea as well as additives which can be used to increase citric acidreactivity. It should be recognized, however, that it is very possiblethat utilizing an additive to increase one of the values will alsoincrease the other and that the additives will typically be selectedbased on the desired outcome from the initial lime feed.

To increase BET surface area specifically, glycols derived from ethyleneoxide such as, but not limited to, diethylene glycol or amines producesfrom reacting ethylene oxide with ammonia such as, but not limited to,tri-ethanolamine can be added to the slaking water. Either of these whenadded in levels of between about 0.5-3% by weight to the quicklime feedwill typically be sufficient to raise a lime hydrate with a BET surfacearea less than or equal to 20 m²/g to a level above that and typicallyat or above 30 m²/g.

These types of compounds are also particularly useful to counteract thenegative effect of using sodium compounds to reduce resistivity. Forexample, utilizing a sodium addition at a rate of 2.3% of quicklime feedwill typically reduce the BET surface area of a hydrate to around 20.Thus, an original hydrate formulation which is well above 20 or 30 canbe reduced below that value quite readily. It has been found that anabout 0.5% addition of diethylene glycol can essentially recover theentire lost amount and an increased addition can actually result in alime hydrate that was formulated to have a BET surface area between 20m²/g and 30 m²/g but was reduced below 20 m²/g due to the sodiumaddition, to now be above 30 m²/g.

As contemplated above, the ability to utilize traditional hydratemanufacturing and then utilize additives to produce what is an HRH isvery valuable. However, in certain applications, being able to producean SRH can also be valuable. For example, if one was to produce a limehydrate which already has a BET surface area above 30 m²/g, one couldnow add the above additives to produce a lime hydrate with a BET surfacearea of 60 m²/g or more.

In order to specifically increase citric acid reactivity in a limehydrate, which is believed to directly correspond to acid gas reactivityas discussed above, sugars, such as, but not limited, to monosaccharides(for example fructose, galactose, and glucose) or disaccharides (forexample lactose, sucrose, and maltose) can be added to the lime hydratesuch as through being provided as part of the slaking water. In anotherembodiment lignosulfonate salts (such as, but not limited to, calciumlignosulfonate) can alternatively or additionally added. Regardless ofthe material used, the additional levels will generally be about 0.75%to 1.25%, preferably about 1% of the CaO feed by weight.

Again, the ability to utilize traditional hydrate manufacturing and thenutilize additives to produce what is an HRH is very valuable. However,an SRH can also be manufactured by applying the above additives to anHRH manufactured, for example, in accordance with the United Statespatents and patent applications referenced previously. By inclusion ofcitric acid reactivity increasing compounds, the citric acid reactivityof HRH can be further increased. This allows for the creation of an SRHagain and allows for a compound that can be used for activities thatwere previously not possible. It is believed that SRH is particularlyvaluable for in-flight neutralization and particularly in applicationswhere contact times are very short or for applications outside acid gasneutralization in flue gas.

As should be apparent to one of ordinary skill, an embodiment of thepresent systems and methods also includes taking an existing HRH ortraditional lime hydrate and adding both sets of additives to it. Thiscan provide for increases in both parameters and produce a particularlyreactive material.

HRH and SRH as discussed above could be used as part of a dry sorbentinjection system into the off gas of an industrial plant, incinerator,or boiler that combusts sulfur and/or halogenated fuels. The DSI systemfor injecting hydrates will generally comprise a storage silo, feedvalve, and a means of conveyance of the product that could usepressurized gas or vacuum. The conveying gas/hydrate mixture is conveyedwithin a pipe and fed into the flue gas stream to be treated. There canbe one or multiple feed points into the flue gas as contemplated in FIG.1 at points (201), (203), and/or (205) for example. The hydrate willgenerally be injected at temperatures below 2400° F. for capture of SO₂and at temperatures below 1100° F. for capture of SO₃ and/or halogenatedacids. However, this is not required.

HRH and SRH is beneficial especially when the end user can capitalize onthe HRH's ability to rapidly neutralize acid gases or other targetmolecules in-flight, i.e., prior to forming a bed upon bags of a fabricfilter or plates of an ESP. HRH can also provide benefit where a userneeds to achieve high level removal in a short time and does not havethe luxury of a long duct run. This can be particularly valuable wherethere is co-injection or HRH or SRH with a mercury sorbent where SO₃must be removed prior to the mercury sorbent injection, and inapplications with a short residence time prior to a small ESP (e.g.,where point (205) is part of a short duct).

The qualifier “generally,” and similar qualifiers as used in the presentcase, would be understood by one of ordinary skill in the art toaccommodate recognizable attempts to conform a device to the qualifiedterm, which may nevertheless fall short of doing so. This is becauseterms such as “planar” are purely geometric constructs and no real-worldcomponent is a true “plane” in the geometric sense. Variations fromgeometric and mathematical descriptions are unavoidable due to, amongother things, manufacturing tolerances resulting in shape variations,defects and imperfections, non-uniform thermal expansion, and naturalwear. Moreover, there exists for every object a level of magnificationat which geometric and mathematical descriptors fail due to the natureof matter. One of ordinary skill would thus understand the term“generally” and relationships contemplated herein regardless of theinclusion of such qualifiers to include a range of variations from theliteral geometric or similar meaning of the term in view of these andother considerations.

While the invention has been disclosed in conjunction with a descriptionof certain embodiments, including those that are currently believed tobe the preferred embodiments, the detailed description is intended to beillustrative and should not be understood to limit the scope of thepresent disclosure. As would be understood by one of ordinary skill inthe art, embodiments other than those described in detail herein areencompassed by the present invention. Modifications and variations ofthe described embodiments may be made without departing from the spiritand scope of the invention.

It will further be understood that any of the ranges, values,properties, or characteristics given for any single component of thepresent disclosure can be used interchangeably with any ranges, values,properties, or characteristics given for any of the other components ofthe disclosure, where compatible, to form an embodiment having definedvalues for each of the components, as given herein throughout. Further,ranges provided for a genus or a category can also be applied to specieswithin the genus or members of the category unless otherwise noted.

1. A method for forming a sorbent composition with improved acid gasreactivity comprising: forming a calcium oxide particulate; slaking saidcalcium oxide particulate with water including an additive to formcalcium hydroxide particles; and forming a sorbent composition from saidcalcium hydroxide particles; wherein said additive is selected from thegroup consisting of: glycols derived from ethylene oxide and aminesproduced from reacting ethylene oxide with ammonia; wherein saidadditive is provided at a ratio of between 0.5% to 3% of said calciumoxide feed by weight. wherein said calcium hydroxide particles have areactivity of less than 10 seconds and a BET surface area of 20 m²/g orgreater; and wherein said reactivity is an amount of time it takes saidcalcium hydroxide particles to neutralize in citric acid, said citricacid having a mass greater than 10 times a mass of said calciumhydroxide particles.
 2. The method of claim 1 wherein said reactivity isless than 8 seconds.
 3. The method of claim 1 wherein said reactivity isless than 4 seconds.
 4. The method of claim 1 wherein said reactivity isless than 3 seconds.
 5. The method of claim 1 wherein said reactivity isbetween about 2 seconds and about 5 seconds.
 6. The method of claim 1wherein said mass of said calcium hydroxide particles is about 1.7 gramsand mass of citric acid is about 26 grams.
 7. The method of claim 6wherein said reactivity is less than 8 seconds.
 8. The method of claim 6wherein said reactivity is less than 4 seconds.
 9. The method of claim 6wherein said reactivity is less than 3 seconds.
 10. The method of claim6 wherein said reactivity is between about 2 seconds and about 5seconds.
 11. The method of claim 1 wherein said calcium hydroxideparticles have a BET surface area of 30 m²/g or greater.
 12. The methodof claim 11 wherein said calcium hydroxide particles have a BET surfacearea of 40 m²/g or greater.
 13. The method of claim 1 wherein saidsorbent composition comprises at least 95% calcium hydroxide particles.14. The method of claim 1 further comprising: wherein said water alsoincludes a compound selected from the group consisting of: sugars andlignosulfonate salts.
 15. The method of claim 1 wherein said additivecomprises diethylene glycol.
 16. The method of claim 1 wherein saidadditive comprises tri-ethanolamine.
 17. The method of claim 1 whereinsaid additive is provided at a ratio of about 0.5% of said calcium oxidefeed by weight.